Method of casehardening vanadium and vanadium alloys

ABSTRACT

A METHOD OF CASEHARDENING VANADIUM AND VANADIUM ALLOYS CONSISTING PREDOMINANTLY OF VANADIUM BY HEATING THE MATERIAL BRIEFLY AT 1100 TO 1300*C. IN AN ATMOSPHERE OF ARGON SATURATED WITH WATER VAPOR.

United States Patent O sented by the United States Atomic Energy Commission Filed Mar. 7, 1969, Ser. No. 805,384 Int. Cl. C2111 1/74 US. Cl. 14820.3 1 Claim ABSTRACT OF THE DISCLOSURE A method of casehardening vanadium and vanadium alloys consisting predominantly of vanadium by heating the material briefly at 1100 to 1300 C. in an atmosphere of argon saturated with water vapor.

CONTRACTUAL ORIGIN OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

BACKGROUND OF THE INVENTION Metals such as titanium, zirconium, vanadium and tantalum are very resistant to attack by certain chemical agents while having relatively high melting points. These metals, and alloys thereof, are, therefore, suitable for use as materials of construction in the chemical industry. Unfortunately, these same materials are not hard enough without treatment for use where wear is a factor, such as in valves, nozzles, orifice plates and the like.

Various procedures are known for casehardeni-ng these materials, all of which involve controllably diffusing oxygen, carbon and/ or nitrogen into the metal lattice. Vanadium and alloys consisting predominantly of vanadium are difficult to caseharden, because vanadium reacts quite readily with oxygen; thus attempts to caseharden vanadium usually result in oxidation of the metal rather than controlled diffusion of oxygen into the metal.

SUMMARY OF THE INVENTION According to the present invention, controlled diifusion of oxygen into vanadium and vanadium alloys to obtain a hardened case is accomplished by heating the material briefly in an atmosphere of argon saturated with water vapor at 1100 to 1300" C. This procedure ensures that the material will be contacted by a limited, controllable amount of oxygen for diffusion into the case.

BRIEF DESCRIPTION OF THE DRAWING The single figure of the drawing is a graph in which hardness is plotted as a function of position in test specimens which have been subjected to differing heat treatments.

DESCRIPTION OF THE PREFERRED EMBODIMENT All of the test specimens employed in the tests described hereinafter were vanadium-20% titanium rods. The rods used in Examples l-6 were 0.223" in diameter and 3%." in length, while the rods used in Examples 7 and 8 were 0.218" in diameter and 2 /2" in length. The first-mentioned rods had been rolled to a diameter of 0.260", swaged to a diameter of 0.242", annealed at 900 C. for one hour, and then centerless ground to a diameter of 0.323". A smili-ar procedure was used to prepare the rods used in Examples 7 and 8. The original hardness of all rods was about DPH 260. In all tests, the equipment was purged with argon for five minutes and the hardness measured on opposite sides of the red at & intervals along the rod using a IO-kilogram weight in an A-very hardness tester.

Example 1 Heated at 1525 C. for one minutetotal heat cycle, five minutescooled ten minutes in argon.

Diamond pyramid hardness Distance from One side Opposite end of rod of rod side of rod Average Example 2 Heated at 1475-l500 C. for one minute in a container having a pool of water in the bottomtotal heat cycle, six minutesquenched in the water at the bottom of the container.

Diamond pyramid hardness Heated at l500l520 C. for one minute-total heat cycle, four minutes-end quenched for five minutes with 745 cc./min. of water through & outlet disposed /s" below test specimenshield located 1" from the water orifice to prevent splashing of water on the sides of the rod.

Diamond pyramid hardness Distance from One side Opposite end of rod of rod side of rod Average Example 4 Heated at 1400-1425 C. for one minute-total heat cycle, four minutes-end quenched for five minutes with 700 cc./min. of water through V outlet disposed 4;" Example 8 below test specimen. A shield was used.

Heated at 1300 C; for one minute-total heat cycle,

Diamond pyramid hardness four minutescooled five minutes in argon that had been Distance from one Side Opposite bubbled through water. The argon was introduced at the end of rod of rod side erred Average bottom of the teest container so as to impinge on the end 464 464 464 of the test rod. 401 401 401 366 401 384 866 394 330 351 380 366 Dlamond pyramid hardness 351 357 354 10 322 357 340 Distance from One side Opposite 317 339 328 end of rod of rod side of rod Average 317 339 323 231 330 305 681 734 707 281 314 293 734 792 763 281 306 294 734 792 763 274 231 27s 734 542 642 606 433 543 572 421 495 Example 5 514 366 441 433 330 405 Heated at 1300-1325 C. for one minute-total heat 437 322 377 409 322 367 cycle, four m1nutesend quenched for five minutes with 366 322 343 750 cc./min. of water through outlet disposed 336 309 322 322 302 312 below test specimen. A shield again was used.

Diamond pyramid hardness Th e results of these tests are given graphically in the Digtaincerom g 3P Avera e drawing. It is evident at a glance that the test samples en 0 r0 0 m S 80 o g heated in argon containing water vapor are much harder Z2? fig g than those heated in argon which does not contain water 401 421 411 vapor. Example 1 shows that heat treating a vanadiumggg 33% 2 5, 20% titanium rod at 1525 C. for one minute does not 4 383 365 greatly affect the hardness of the alloy. Similarly, end gig, 228 gig quenching samples which had been heated in an argon 317 342 330 atmosphere which did not contain water vapor-see Ex- 332 3 38g amples 3, 4 and 5increased the hardness only slightly. 274 294 234 In Examples 2, 6, 7 and 8 the test samples were heated 274 274 in an argon atmosphere containing water vapor and in ever case the hardness of the alloy is greatly increased. Example 6 It will be appreciated that the rapid decrease in hardness Heated at 1500 C. for one minute in a ntain r havalong the length of the test rods in some of the examples ing a pool of water in the bottom-total heat cycle, five 18 due to the experimental approach. In Examples 2, 6

minutes-quenched in th water t th b tt of the 40 and 7 the rod was heated while disposed vertically in a container containing water. Thus there was a higher procontainer.

portion of water vapor in the container at the lower end Diamond pyramid hardness of the rod than at the top and, as expected, the lower end Distance from mm of the rod was harder than the upper end of the rod. In end of rod of rod side or rod Average Example 8 argon saturated withwater vapor was intro- 1 097 1 081 1,089 duced into the bottom of the container so as to impinge 1: 064 s70 970 on the bottom of the test rod. Examples 7 and 8 prove $33 a: gig that the increased hardness is caused by the water vapor 2 2 fig in the atmosphere, since increased hardness is obtained 548 413 478 both by heating the test sample over water and by saturati g 41% 22:; ing the argon with water vapor before admitting it into 464 413 438 the test container. Tests 2 and 6 prove that completely 4%: 322 fig quenching the test sample in water does not adversely 464 366 416 aflFect the hardness. It is noted that in both these examples g} 328 the test samples were heated in argon while suspended 327 322 324 over Water and were then dropped into the water. It is 279 274 276 believed that quenching the sample in water or some other Example 7 inert liquid would be desirable, although this has not as yet been completely proved. Heated at 1500 for 0116 m1nutetta1 heat cycle These tests taken together indicate that oxygen is added four minutes-c00.led 12-5 {minut s in argon Wlth 31/2" to the surface of the test sample when the test sample is of water in bottom of contal rheated in argon containing water vapor. Hardening then Diamond pyramid hardness occurs upon cooling of the sample. A maximum temperature of 1300 C. is specified begg ggfg g gg ggfig g Average cause the grain size increases and plasticity and elongation 946 1 038 991 suifer at higher temperatures. Temperatures lower than 946 11132 1,039 1100" C. may be satisfactory; however, a longer time at 203 38% 5 temperature is needed. 548 508 It will be understood that the invention is not to be g2; :22 13 limited to the details given herein but that it may be modi- 366 464 416 fied within the scope of the appended claim. 345 390 367 The embodiments of the invention in which an exclu- 342 390 367 309 380 345 srve property or privilege 1S claimed are defined as follows: 309 3 8 325 1. A method of casehardening a vanadium-20% titani- 274 239 281 15 um alloy comprising heating the alloy in argon saturated References Cited UNITED STATES PATENTS 2,217,802 10/1940 Koehring 1486.3X 3,111,434 11/1963 Takao et al. 148-13.1 3,314,827 4/1967 Vries 148-13.1

6 OTHER REFERENCES Z. Meta1lkde., vol. 57, 1966, pp. 66-69.

Argonne National Laboratory-Report N0. 6928, W. R.

Burt etaL, pp. 9-11, 68, 73-75.

CHARLES N. LOVELL, Primary Examiner US. Cl. X.R. 148-63, 31.5 

